Volume 25, Issue 3 (September 2002)

The Quality of Continuous Soil Samples

The quality of continuous soil samples from four typical Irish soft ground strata is studied. It was found that the MOSTAP® continuous specimens have lower initial moisture content and higher bulk density than block or tube samples. Test data from MOSTAP® samples underestimate 1D yield stress ratio, compression in the normally consolidated range and creep. Triaxial tests on the MOSTAP® specimens show erratic results. For the clays studied, they give lower undrained strength, a higher strain to failure, and a larger small strain stiffness than block samples. MOSTAP® specimen quality, however, improves with reducing soil sensitivity and increasing soil strength. These results are caused by the MOSTAP® sampler having an inferior cutting head geometry, leading to increased destructuring of the soils. In silt materials, the sampler penetration is partially drained, leading to densification of material, the effects being greatest for the MOSTAP® sampler. Recommendations are given for possible improvements to the sampler.